Differentiate tag search behavior for search vs. retrieve

- There are two contexts in which a tag may be retrieved; one is using a search from the search menu, in which case we want to do fuzzy matching, including support for wildcard characters. The other is when a user clicks on a tag name on a record. In this case, we want to do exact matching, because the user has selected a specific known entity. These changes enable the code to tell the search case from the standard click case with the use of a hidden filter applied by the search controller.